Method and apparatus for converting chemical energy stored in wastewater

ABSTRACT

A method and apparatus is provided for harvesting electricity from a biofilm retained in a zero chamber, no interphase container, the biofilm having a portion supporting aerobic microbial activity and a second portion supporting anaerobic microbial activity, wherein the first and the second portion are in direct physical contact. A ground or a power harvester is electrically connected, directly or indirectly, to the second portion of the biofilm.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a method and apparatus for convertingchemical energy stored in wastewater, and particularly to a zerochamber, no interface system which can provide oxidation of carbonaceousmatter in the wastewater as well as selectively electricallyinterconnect a biofilm to a power harvester or ground.

Description of Related Art

The use of microbial fuel cells (MFCs) to generate electricity fromorganic substances provides numerous benefits including operation atambient temperatures and pressures. Moreover, because the oxidationreactions which occur in a MFC typically do not require aeration, MFCsgenerally have reduced power requirements. The lack of aeration mayhamper the breakdown of organic compounds (Cheng H et al. 2015 WaterResearch 81(72-83) in traditional chambered MFCs).

Traditional two-chamber MFCs typically use an anode chamber and aseparate cathode chamber. In general, these chambers are separated by aproton exchange membrane (PEM) and are electrically connected through anexternal circuit. In the anode chamber, bacteria generate electrons andgain energy for growth by oxidizing available nutrients. Electricity isthen typically produced by transferring the generated electrons to theanode. Protons created as a result of the oxidation migrate through theproton exchange membrane and combine with the electrons in the presenceof oxygen at the cathode to form water in the cathode chamber. In suchMFCs, the electrodes may include various forms of conductive material,for example carbon paper or carbon cloth, such as those manufactured bythe E-TEK Division of BASF Fuel Cell, Inc. while materials such as asulfonated tetrafluorethylene copolymer (e.g., Nafion) may be used asexchange membranes in two-chamber MFCs. Electrodes may be furtherenhanced with catalysts, such as platinum (Pt), to improve theirperformance.

A single-chamber MFC includes an open ended chamber having both an anodeand a cathode, but lacks an exchange membrane. The two electrodes aretypically fixed at opposite ends of the chamber, with the anode embeddedat the base of the chamber, and a two-sided cathode forming aninterphase with a water-tight seal on an end of the chamber, wherein thechamber is filled with biodegradable nutrients and bacteria.

While the single-chamber MFC offers benefits over the two chamber MFC,the single-chamber MFC still requires two electrodes, typically ofspecialty materials. The single chamber MFC also creates the interphase,wherein one face of the cathode is exposed to the air while a secondface of the cathode is exposed to the wastewater, wherein the interphaseprovides a passage for oxygen diffusion. In addition, the electrodespacing in these systems restricts scaling the chambers to commercialsizes or capacities.

BRIEF SUMMARY OF THE INVENTION

The present disclosure provides a zero compartment, no interphase fuelcell, wherein electric current is harvested from a biofilm to anelectrical ground.

In one configuration, a method is provided including forming a biofilmon a substrate exposed to wastewater having dissolved oxygen, thebiofilm having a sufficient thickness to define a gradient betweenaerobic microorganisms (bacteria) exposed to the wastewater andanaerobic microorganisms (bacteria) proximal to the substrate; andelectrically connecting the anaerobic microorganisms (bacteria) to apower harvester.

In a further configuration, a microbial fuel cell is provided having acontainer for retaining a volume of wastewater, the wastewater includingdissolved oxygen; a substrate at least partially submerged in thewastewater, the substrate supporting a biofilm exposed to the volume oforganic wastewater, the biofilm having a sufficient thickness to definean electron concentration gradient between microorganisms (bacteria)exposed to the wastewater and microorganisms (bacteria) proximal to thesubstrate; a power harvester; and a first electrical conductor betweenthe power harvester and one of (a) the biofilm and (b) the substrate.

Also provided is a microbial fuel cell having a container retaining avolume of wastewater, the container being free of a proton exchangemembrane and the wastewater including dissolved oxygen; a substrate atleast partially submerged in the wastewater, the substrate supporting abiofilm exposed to the volume of organic wastewater, the biofilm havinga sufficient thickness to define an oxygen concentration gradientbetween microorganisms (bacteria) exposed to the wastewater andmicroorganisms (bacteria) proximal to the substrate; a power harvester;a first electrical conductor between the power harvester and one of (a)the biofilm and (b) the substrate; and a second electrical conductorbetween the power harvester and a ground.

In another configuration, a method is provided including forming abiofilm on a substrate exposed to wastewater having dissolved oxygen,the biofilm having a sufficient thickness to define a gradient betweenaerobic microorganisms (bacteria) exposed to the wastewater andanaerobic microorganisms (bacteria) proximal to the substrate; andelectrically connecting the anaerobic microorganisms (bacteria) to atleast one of a ground, an electrical resistance, an electrical load or apower harvester.

In yet another configuration, a microbial fuel cell is provided having acontainer for retaining a volume of wastewater, the wastewater includingdissolved oxygen; a substrate at least partially submerged in thewastewater, the substrate supporting a biofilm exposed to the volume oforganic wastewater, the biofilm having a sufficient thickness to definean electron concentration gradient between microorganisms (bacteria)exposed to the wastewater and microorganisms (bacteria) proximal to thesubstrate; and a first electrical conductor between at least a portionof the biofilm and one of (a) a ground and (b) a power harvester.

Also provided is a configuration having a microbial fuel cell having acontainer retaining a volume of wastewater, the container being free ofa proton exchange membrane and the wastewater including dissolvedoxygen; a substrate at least partially submerged in the wastewater, thesubstrate supporting a biofilm exposed to the volume of organicwastewater, the biofilm having a sufficient thickness to define anoxygen concentration gradient between microorganisms (bacteria) exposedto the wastewater and microorganisms (bacteria) proximal to thesubstrate; and a first electrical conductor electrically connecting thebiofilm to one of (a) a ground (b) a power harvester.

The following will describe embodiments of the present disclosure, butit should be appreciated that the present disclosure is not limited tothe described embodiments and various modifications of the invention arepossible without departing from the basic principles. The scope of thepresent disclosure is therefore to be determined solely by the appendedclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic representation of the present system.

FIG. 2 is a front view of a representative substrate.

FIG. 3 is a side view of the representative substrate of FIG. 2.

FIG. 4 is a top view of the representative substrate of FIG. 2.

FIG. 5 is an enlarged front view of a portion of the representativesubstrate.

FIG. 6 is an enlarged side view of a portion of the representativesubstrate.

FIG. 7 is a schematic representation showing representative scaling.

FIG. 8 is a flow chart of a method encompassing the present process.

FIG. 9 is a schematic of an array of an alternative representativescaling.

FIG. 10 is a schematic cross section of a biofilm.

FIG. 11 is a schematic representation of an alternative configuration ofthe present system.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the present disclosure, the term “aerobic” refers toconditions in a container, or containers, where there is an amount ofdissolved oxygen sufficient to sustain an aerobic microbial growth.

For purposes of the present disclosure, the term “anaerobic” refers toconditions in a container, or containers, where oxygen is absent orthere is insufficient oxygen to (i) provide aerobic microbial activityor (ii) poison anaerobic microbial activity. Often, anaerobic conditionsrefer to an environment where only anaerobic microorganisms can survive.

For purposes of the present disclosure, the term “biofilm” refers to anaggregate of living micro-organisms which are connected and/orimmobilized onto a substrate as microbial colonies. The microbes aretypically embedded within a self-secreted matrix of extracellularsubstance. Biofilms may form on living, non-living, organic, orinorganic substrates. The present biofilms are electroactive biofilms asthey possess specific electroactive properties such as electrongeneration.

For purposes of the present disclosure, the term “container” refers tovessels or reservoirs that support a biologically active microbialenvironment, and typically retain a volume of wastewater and/or allowfor biomass conversion via microorganism metabolism within thecontainer. A container may provide for various macro-environmentalconditions, such as, but not limited to, gas content, e.g., air, oxygen(or lack of oxygen), nitrogen (or lack of nitrogen), carbon dioxide,flow rates, temperature, pH, light intensity, and agitationspeed/circulation rate. Containers can be of any size, shape, ormaterial, and of any configuration that will physically retain asufficient volume of wastewater capable of sustaining a biofilm capableof electricity generation. Acrylic compartments, for example, aresuitable for smaller, laboratory scale embodiments, while compartmentsmade of steel may also be used in large scale production.

For purposes of the present disclosure, the term “electrode” refers toan anode or a cathode. The “anode” is an electrode that facilitates theoxidation, i.e., the loss of electrons, of various nutrients in biomass.For example, the wastewater may contain one or more saccharides whichare oxidized by bacteria, i.e., electrogenic bacteria, at the anode. The“cathode” is an electrode that facilitates the reduction, i.e., gainingof electrons, of an oxidant, typically oxygen.

For purposes of the present disclosure, the term “wastewater” 70 refersto, but is not limited to, groundwater, contaminated groundwater,sewage, graywater, landfill leachate, sugar refinery waste, paperpulping waste, bakery waste, brewery waste, fluid compositionscontaining bacterial factors, organic matter, wood or wood waste, straw,herbaceous crops, corn stover, grass such as switch grass, or othersources of annual or perennial grass, paper or paper waste, pulp andpaper mill waste, municipal and/or industrial solid wastes, and/or fluidcompositions comprising bacterial factors, or any combination thereofhaving organic and/or inorganic compounds or materials that contain asource of energy for bacteria, e.g., electrogenic bacteria. Thewastewater 70 typically contains waste contaminants that are broken downinto simple sugars and other bioconstituents to support electrogenicculture growth in the present container. As such, in concert with theelectrogenic cultures, the wastewater 70 provides a supply of electronsfor generating electricity while sustaining electrogenic bacterialculture growth and metabolism. Further, the wastewater 70 is aerobic oroxygen carrying, having in certain configurations, a dissolved oxygencontent at least 1.0 mg/L. The oxygen level is sufficient to sustainaerobic microbial activity within the container 10.

“Cultured” microorganisms include those grown and developed in any ofthe known growth media cultures, such as but not limited to Bennett'smedium, Marine broth, Mannitol agar and nutrient agar. Culturing isperformed and modified, as desired, for suitable applications requiringa particular density and/or confluence, which can be for about 1 to 50days. For example, as known, the bacteria are cultured until a desiredcell density is attained.

Referring to FIG. 1, the present system includes a container 10 and asubstrate 30 supporting a biofilm 50 in a volume of wastewater 70.

In select configurations, the biofilm 50 is electrically connected to aload, such as but not limited to a power harvester 80 as set forthbelow. It is understood the biofilm 50 can be electrically connected toa ground, an electrical resistance or the power harvester 80.

Although not required, it is anticipated that for purposes of automationa plurality of sensors 20, such as temperature, pH, oxygen sensors,current or voltage meters can be operably connected to the wastewater(either upstream, downstream, or within the container) and/or thebiofilms 50. The sensors 20 can include sensors to detect any parameterof the wastewater 70 including those above as well as chemicalconstituents, conductivity, sound velocity or any other characteristicof the wastewater. In select configurations, the system can furtherinclude flow control devices 24, such as valves.

In addition, select configurations can include an aerator 12 located toincrease dissolved oxygen in the wastewater 70 as well as heaters 14 andchillers 16 for selectively heating or cooling the wastewater.

In these further select configurations, a controller 90 can be operablyconnected, either wirelessly or wired, to the sensors 20, the flowcontrol devices 24, the aerator 12, the heaters 14, the chillers 16, andthe power harvester 80.

The container 10 defines a zero chamber microbial (microorganism) fuelcell (MFC), as the container does not include membranes orelectrochemical dividers. In addition, select configurations of thecontainer 10 do not include an interphase. However, it is understood thecontainer 10 may include or define compartments wherein the compartmentsare fluidly connected and share a common flow of wastewater 70. Thecontainer 10 can be formed of any of a variety of the materialsincluding electrically conductive, such as metal or alloy ornonconductive, such as polymeric.

The container 10 includes an inlet 11 for receiving wastewater 70 and anoutlet 13 for passing wastewater. The container 10 can be open topped orclosed, wherein the inlet 11 and the outlet 13 are physically spacedapart in the container. It is contemplated the inlet 11 and outlet 13can be integrally formed with the container 10 or provided bycorresponding pipes providing an inlet of wastewater 70 and the outletof wastewater. Inlet and outlet valves 24 are operably connected to therespective inlet 11 and outlet 13 for selectively controlling the flowof wastewater 70 in, or through, the container 10.

The container 10 does not include an interphase for oxygen diffusion.Thus, the container 10 does not require expensive oxygen permeablematerials and can be readily scaled as it merely needs to retain adesigned volume and/or flow of wastewater.

It is understood an array of containers 10 can be employed as seen inFIG. 9, wherein the flow through the containers is serial or parallel,depending in part on the constituents of the wastewater and microbialmakeup of the biofilms 50. Thus, in one configuration the outlet of afirst container is connected to the inlet of a second container.Alternatively, an inlet manifold can be used to distribute availablewastewater to a plurality of containers. Similarly, an outlet manifoldcan be employed to release wastewater from the array.

The containers 10 are not constrained by different requirements of thewastewater 70. That is, no preconditioning step is required prior tointroduction of a container 10 or a given container within the containerarray. The volume of an individual container 10 or container array canbe any size as determined by the anticipated volume or flow ofwastewater 70.

As set forth above, one configuration employs wastewater 70 having amaterial dissolved oxygen content, and particularly a content of atleast 1.0 mg/L. However, it is understood, the dissolved oxygen contentcan be supplemented or imparted by bubbling air through the wastewater70 prior to entering the container 10, while in the container or bothprior to entering and within the container.

The flow of wastewater 70 through the container 10 can be continuous,intermittent or batch. So long as the necessary oxygen content andnutrients for the biofilm 50 are provided, the flow can be selected asdesired.

The substrate 30 is selected to physically support the biofilm 50. Thesubstrate 30 can be conductive or nonconductive. In one configuration,the substrate is a carbon fiber mesh, such as commercial materialMcMaster-Carr 87365K13. Alternatively, the substrate 30 can beconductive such as a wire mesh or even a sheet or a plate. As seen inFIGS. 2-7, a support 32 can be connected to a portion of the substrate30. While the substrate 30 can include catalysts as known in the art, inthe present configuration, a catalyst is not necessary, thus thesubstrate can be catalyst free.

While the substrate 30 is shown as a substantially planar member as seenin FIGS. 2-7, it is understood the substrate can be sufficientlyflexible or bendable to be folded or convolute. In alternativeconstructions, a flexible planar substrate 30 can be wound or formedinto a spiral profile. This increases the area/volume of biofilmrelative to container volumes.

The biofilm 50 is supported by or carried by the substrate 30 andincludes a first portion 52 supporting aerobic microbial activity and asecond portion 54 supporting anaerobic microbial activity, wherein thefirst and the second portion are in direct physical contact. In oneconfiguration, the first portion 52 of the biofilm 50 overlies thesecond portion 54 of the biofilm and substantially precludes exposure ofthe second portion to dissolved oxygen in the wastewater. In thisconfiguration, the biofilm 50 includes an aerobic layer 52 and ananaerobic layer 54, wherein the aerobic layer is exposed to thewastewater 70 and sufficiently covers or overlays the anaerobic layer topreclude aerobic activity in the anaerobic layer. That is, the aerobiclayer 52 effectively creates the anaerobic layer 54 as available oxygencannot pass through the aerobic layer to the anaerobic layer.

In one configuration, the biofilm 50 includes electrogenic bacteriacapable of moving electrons to solid phase materials includingelectrodes through the breakdown of organic matter, wherein the electrontransfer is to the surrounding environment, i.e., an anode, rather thanan electron acceptor such as oxygen. Such electrogenic bacteria arecapable of completely oxidizing organic compounds to carbon dioxide orother byproducts and then transferring the electrons derived from theoxidation to a remaining portion of the biofilm. Thus, the biofilm 50can oxidize, and hence biodegrade organic matter such carbonaceousmatter found in the wastewater 70.

It is contemplated the boundary between the aerobic layer 52 and theanaerobic layer 54 may be defined by a gradient, wherein the dimensionof the gradient is relatively small, less than ⅓ of the thickness of thebiofilm 50. In one configuration, the biofilm 50 has a thickness betweenapproximately 0.5 mm to approximately 0.75 mm. However, it is understoodthe thickness of the biofilm 50 is at least partly dictated by thecontent of the wastewater 70 as well as the makeup of the biofilm.

The biofilm 50 defines a free electron concentration gradient betweenthe aerobic layer 52 and the anaerobic layer 54, as schematically shownin FIG. 10. In one configuration, this electron gradient is directly (byan electrical conductor) or indirectly (through the substrate)electrically connected to the power harvester 80. It is furthercontemplated the electron flow may occur from the anaerobic layer 54, asthis layer acts like a conductor of electrons.

The biofilm 50 can be formed of native, cultured, wild, or anyconfiguration of microbes.

The power harvester 80 can be a low voltage-low current harvesterconnected to any of a variety of commercially available devices thatutilize, convert or store energy from an electron flow. A satisfactorypower harvester 80 includes those sold by Morningstar Corporation ofNewtown, Pa., including the SunSaver™ line of photovoltaic converters.The power harvester 80 also includes a resistive load electricallyintermediate the biofilm and ground.

The electrical connection between the power harvester 80 and the biofilm50 can be provided by an electrical conductor 84, wherein the electricalconductor extends directly from the power harvester to the biofilm, suchas the anaerobic portion, or indirectly to the conductive substrate.Further, the electrical connection of the electrical conductor 84 to thebiofilm 50 can be at a single contact point in the biofilm or at aplurality of contact points.

In those configurations employing an electrically conductive substrate30, the electrical connection between the power harvester 80 and thebiofilm 50 can include the substrate. Thus, the electrical connectionextends between the substrate 30 and the power harvester 80. As in thedirect connection to the biofilm 50, the electrical connection to thesubstrate 30 can be at a single contact point or through a plurality ofcontact points.

The biofilm 50 is electrically connected to the positive (+) terminal ofthe power harvester 80. The negative (−) lead of the power harvester 80is connected to ground. A battery and load can be connected pursuant tothe operating instructions of the power harvester. Thus, only a singleelectrical conductor 84 connects the biofilm 50 to the power harvester80 and a second electrical conductor connection with the container 10,biofilm 50, substrate 30 or wastewater 70 is not necessary.

Referring to FIG. 10, the biofilm 50 includes a sufficient thickness tocreate an electrochemical barrier within the biofilm, wherein asufficient gradient is created between the portion of the biofilmexposed to the oxygen bearing wastewater as the aerobic layer 52 and theunderlying portion of the biofilm that is the anaerobic layer 54. Byvirtue of the oxygen gradient within the biofilm 50 and hence gradientbetween the aerobic microbial activity in the biofilm exposed to thewastewater 70 and the anaerobic microbial activity, an electricalpotential gradient is created within the biofilm. Depending upon thesubstrate 30, the electric potential can be taken from the anaerobiclayer 54 of the biofilm 50 or the substrate 30 (if conductive).

A specific configuration is shown in FIGS. 2-6, wherein the substratesare substantially rectangular having the upper and lower supports 32.While the present substrates 30 are shown having the supports 32, it isunderstood that depending on the particular material of the substrateand the intended exposure to the wastewater 70, the substrates can beself-supporting or connected to a full frame for maintaining theorientation of the substrate within the wastewater.

As stated above and shown in FIG. 7, each substrate 30 can include aplurality of electrical connections to the power harvester 80. Thesubstrates 30, and hence biofilms 50, can be electrically connected inseries or parallel in their electrical connection to the power harvester80.

As each substrate 30 need only be electrically connected to the powerharvester 80, the inclusion of additional substrates does not presentany scaling issues. Further, as each substrate 30 can include aplurality of electrical connections or can include the electricalconductor 84, the size of the available substrates for a given flow rateof wastewater 70 can be readily changed.

The controller 90 is operably connected to the power harvester 80, theaerator 12, the flow controls 24, the heater/chiller 14, 16, and thesensors 20. The controller 90 can be programmed to adjust the flow ofthe wastewater 70 relative to the biofilms 50 as well as possible mixingof wastewater streams to provide a substantially predetermined oxygencontent and nutrient content to the container 10. The controller 90 canbe a dedicated processor or an applicator on a host. The generation ofelectrical current (or voltage) measured by the meters and monitored bythe controller 90 provides an indicator of nutrient consumption (andhence nutrient availability). The controller 90 can then increase flowof wastewater 70 to the biofilms 50 to increase nutrient availability ordecrease flow of wastewater to increase percentage of nutrientsconsumed. Similarly, the controller 90 monitoring the temperature,oxygen level and pH can make corresponding adjustments to thetemperature parameters to increase or maintain an efficiency of thesystem.

The controller 90 can be programmed to provide specific actions inresponse to predetermined readings from the sensors 20. For example, ifthe pH of the wastewater 70 is outside a predetermined range, thecontroller 90 can prompt the addition of alkaline or basic material toadjust the pH, particularly in view of monitored flow rate and microbialactivity.

In operation, the wastewater 70 and the substrate 30 are located withinthe container 10 to contact the substrate with the wastewater. As thebiofilm 50 can be formed from wild microbes, sufficient exposure time isprovided between the wastewater 70 and the substrate 30 to develop thebiofilm having an aerobic layer overlying an anaerobic layer.

The biofilm 50 develops to define the aerobic layer 52 exposed to thedissolved oxygen and nutrients in the wastewater 70, wherein the aerobiclayer overlies a layer of developing anaerobic microbes. As the oxygengradient is created in the biofilm 50, an electrochemical barrier iseffectively formed within the biofilm and an electrical potentialgradient is created across the thickness of the biofilm.

The electrical conductor 84 either directly electrically connects thebiofilm 50, such as the anaerobic layer 54, to the power harvester 80 orindirectly electrically connects the biofilm via the substrate 30, andto the power harvester. A ground lead is then connected to the powerharvester 80. It is contemplated the ground lead of the power harvester80 can be electrically connected to the container 10 or the wastewater70.

The wastewater 70 is then exposed to the biofilm 50 either incontinuous, intermittent or batch flows.

The electrons harvested from the biofilm 50 generate an electricalcurrent which is captured by the power harvester 80. Therefore, incontrast to prior MFC, including single chamber configurations, thepresent system does not employ a membrane, such as a proton exchangemembrane or polymer electrolyte membrane (PEM). As the container 10 isfree of a PEM, the cost as well as the complexity of the physical systemis reduced. As the present electron potential is created within thebiofilm 50 itself, rather than across discrete electrodes as in priordesigns, there is no decrease in performance of the present system frombiofilm growth on a cathode surface.

Further, as the present system is operable in a zero chamberconfiguration, there is no need for separate containers or barriers toharvest the power.

In addition, as the present system employs a single electricalconnection to the container 10, the increased cost and complexity ofelectrode pairs for each container is removed. That is, the presentsystem does not require a separate anode and cathode. The lack of aseparate anode and cathode further reduces the cost and complexity ofthe present system.

Though not meant to be bound to any theory of the operation, it isbelieved the separate electrodes and membranes of the prior devices arefunctionally equivalent to the created electrochemical gradient acrossthe thickness of the biofilm 50, between the aerobic layer 52 and theanaerobic layer 54 of the biofilm 50, as shown schematically in FIG. 10.The surface of the biofilm 50 is in contact with the oxygen dissolved inthe wastewater, while the bottom of the biofilm, which is in contactwith the anode, develops an oxygen deficiency caused by the bacteriawithin the overlying biofilm. The aerobic bacteria consume oxygen duringtheir normal respiration, shielding the interior of the biofilm 50 fromthe available oxygen in the wastewater. This forms an oxygenconcentration gradient between the surface layer and the underlyinglayer of the biofilm 50, as well as an electron concentration gradient,with electrons flowing into the biofilm from the surface of the biofilm.The specific profile of the oxygen and electron gradients are at leastpartly determined by the development of the biofilm as well as theoxygen content of the wastewater 70. The gradients shown are merelyrepresentative.

Filamentous bacteria, acting as electron shunts across the biofilm 50,facilitate the electron flow from the surface of the biofilm towards theanode, creating an electron-rich zone at the cathode of the zero chamberMFC. The present system thus takes advantage of the recognition that anelectrochemical gradient exists within a biofilm 50, wherein anelectrical current can be harvested.

In a further configuration, as seen in FIG. 11, the biofilm 50 iselectrically connected to the electrical conductor 84 which is in turnelectrically connected to ground. In this configuration, the electronflow through the electrical conductor 84 is sufficient to maintain thenecessary biological activity of the biofilm 50.

It is contemplated the electrical conductor 84 can provide the contactwith the ground by connection with at least one of the container, thewastewater 70, a ground terminal as well as through the power harvester80. It is believed the contact of the electrical conductor 84 withground provides sufficient load to maintain the oxidation of organicmatter by the biofilm 50. In one configuration, the electrical conductor84 is grounded to a ground other than the wastewater 70, the containeror the power harvester. Thus, the electrical conductor 84 is groundedexternal to the wastewater 70, the container 10 or the power harvester80.

In this configuration, the controller 90 is operably connected to theaerator 12, the flow controls 24, the heater/chiller 14, 16 and thesensors 20. The controller 90 can also be electrically connected to theelectrical conductor 84, as the electrical conductor is connected toground, thus acting as a ground lead for the power harvester 80. Thecontroller 90 in this configuration can be configured and function asset forth above.

The present system further provides oxidation of biodegradable matter inthe wastewater 70. That is, this biofilm 50 can provide bioremediationof the wastewater 70 including oxidizing carbonaceous biological matter.It is contemplated the biofilm 50 may also oxidize nitrogenous matter,expressly ammonium as well as removing nutrients from the wastewater 70.The removal of ammonia is complete, below the detection limit ofconventional ammonia detection tests.

For example, the biofilm 50 has been found to oxidize Phenol (95%removal efficiency, % R), and Aniline (90% R) as found in wastewater.The degradation of Sulphamethoxazole, a broad-spectrum antibiotic, hasbeen reported to occur in biofilms (Wang L et al. 2016 Water Research88:322-328).

Prior membrane based, aerated bioreactors are costly in creation,maintenance, and operation. It has been found the present biofilm 50(typically with substrate 30) forms an open system that can be operatedin a variety of activated sludge environments to provide theoxidization. Thus, the substrate 30 and biofilm 50 can be inserted ordropped into an existing activated sludge environment or wastewaterstream to provide the oxidization of the organic matter, and hencegeneration of electricity (if employed with a power harvester 80),without requiring barriers in the cell, such as PEMs or interphases.

The present system provides a single electrode in contact with thewastewater 70 or the container 10, wherein only a ground is necessary,such as (i) through the power harvester 80 to harvest power in the formof an electron flow from the biofilm 50; or (ii) directly to an externalground. In one configuration, the anode is covered with the biofilm 50and the effective cathode is an electric ground. The zero-compartmentsMFC has one electrode, the anode, and no distinct compartments orinterphase. The anode is covered by the biofilm 50, and the “virtual”cathode is an electric ground. An electric current between the anode andground is created by oxidation reactions occurring within the biofilm,wherein the ground can be a direct grounding, an external ground or viathe power harvester 80.

This disclosure has been described in detail with particular referenceto a presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the disclosure. The presently disclosed embodiments are thereforeconsidered in all respects to be illustrative. The scope of thisdisclosure is indicated by the appended claims, and all changes thatcome within the meaning and range of equivalents thereof are intended tobe embraced therein.

The invention claimed is:
 1. A method comprising: (a) forming a biofilmon a substrate exposed to wastewater that is contained in a containerand having dissolved oxygen, the biofilm having a sufficient thicknessto define a gradient between aerobic microorganisms exposed to thewastewater and anaerobic microorganisms proximal to the substrate; and(b) grounding the biofilm to a ground, the ground being external to thecontainer and the wastewater.
 2. The method of claim 1, whereingrounding the biofilm includes connecting an electrical conductor to thebiofilm and the ground.
 3. The method of claim 1, wherein grounding thebiofilm includes connecting an electrical conductor to the biofilm andthe ground.
 4. The method of claim 1, wherein grounding the biofilmincludes electrically connecting the substrate to the ground.
 5. Themethod of claim 1, wherein the volume of wastewater is independent of aPEM membrane.
 6. The method of claim 1, wherein the volume of wastewateris independent of a catalyst.
 7. The method of claim 1, wherein thecontainer is independent of an interphase for oxygen diffusion.
 8. Themethod of claim 1, wherein the wastewater is organic.
 9. The method ofclaim 1, wherein grounding the biofilm includes electrically connectinga portion of the anaerobic microorganisms to a ground.
 10. A microbialfuel cell comprising: (a) a container for retaining a volume ofwastewater, the wastewater including dissolved oxygen; (b) a substrateat least partially submerged in the wastewater, the substrate supportinga biofilm exposed to the volume of organic wastewater, the biofilmhaving a sufficient thickness to define an electron concentrationgradient between microorganisms exposed to the wastewater andmicroorganisms proximal to the substrate; and (c) a first electricalconductor between a ground and one of (i) the biofilm and (ii) thesubstrate, the ground being external to the container and thewastewater.
 11. The microbial fuel cell of claim 10, wherein thesubstrate is conducting.
 12. The microbial fuel cell of claim 10,wherein the substrate is non-conducting.
 13. The microbial fuel cell ofclaim 10, wherein the container is independent of a proton exchangemembrane.
 14. The microbial fuel cell of claim 10, wherein the containeris independent of a catalyst.
 15. The microbial fuel cell of claim 10,wherein the container is independent of an interphase for oxygendiffusion.
 16. The microbial fuel cell of claim 10, wherein thecontainer is independent of a membrane compartment.
 17. A microbial fuelcell comprising: (a) a container retaining a volume of wastewater, thecontainer being free of a proton exchange membrane and the wastewaterincluding dissolved oxygen; (b) a substrate at least partially submergedin the wastewater, the substrate supporting a biofilm exposed to thevolume of organic wastewater, the biofilm having a sufficient thicknessto define an oxygen concentration gradient between microorganismsexposed to the wastewater and microorganisms proximal to the substratewherein the gradient is sufficient to generate sufficient freeelectrons; and (c) a first electrical conductor between a ground and oneof (a) the biofilm and (b) the substrate, the ground being external tothe container and the wastewater.
 18. The microbial fuel cell of claim17, wherein the substrate is conducting.
 19. The microbial fuel cell ofclaim 17, wherein the substrate is non-conducting.
 20. The microbialfuel cell of claim 17, wherein the ground lead is a common electricalground.
 21. The microbial fuel cell of claim 17, wherein the chamber isindependent of a proton exchange membrane.
 22. The microbial fuel cellof claim 17, wherein the chamber is independent of a catalyst.
 23. Themicrobial fuel cell of claim 17, wherein the chamber is independent ofan interphase for oxygen diffusion.
 24. The microbial fuel cell of claim17, wherein the chamber is independent of a membrane compartment.